Lamp failure detector assembly

ABSTRACT

A lamp failure detector assembly includes a plurality of lamp filament sensors. Each lamp filament sensor includes a switching circuit which is connected to an associated pilot lamp to be monitored and to a transducer which is capable of assuming one of two states. In one state of the transducer, the switching circuit causes a current having one level to flow through the lamp, the level being sufficient to visibly light the lamp. In the other state of the transducer, the switching circuit causes a current to flow through the lamp which is insufficient to visibly light the lamp. A control circuit is connected to the pilot lamp to be monitored - the control circuit being so arranged so as to cause a monitoring current to flow through the pilot lamp when the filament of the latter is good irrespective of the state of the transducer, the monitoring current which passes through the bulb and through the control circuit having a level sufficient to be detected by the control circuit yet insufficient to visibly light the lamp. Each control circuit of a respective lamp filament sensor is arranged to sense the level of current flow through an associated pilot lamp and for generating a control signal when current flow through the pilot lamp is interrupted. A failure sensing circuit is connected to each of the control circuits for receiving a control signal when one of the monitored pilot lamps fails and for energizing a failure indicator lamp as well as an audible alarm device. A ring-back circuit connected to the failure sensing circuit is connectable to the audible alarm device so that when the audible alarm device is connected to the ring-back circuit while one of the monitored pilot lamps is faulty, the audible alarm device is not energized. When the faulty pilot lamp is replaced by a good lamp, the failure sensing circuit and the ring-back circuit change their respective states so that the failure indicator lamp is deenergized and the audible alarm device is energized. The latter energization of the audible alarm device is termed the ring-back and gives an indication that a faulty bulb has been replaced by a good one - the ringing back being continued until the audible alarm device is again connected to the failure sensing circuit.

United States Patent [1 1 Schacket 11] 3,825,914 [451 July 23,1974

1 1 LAMP FAILURE DETECTOR ASSEMBLY [75] Inventor: Robert Schacket, Laurelton, NY. [73] Assignee: Electrospace Corporation, North Bergen, NJ.

[22] Filed: Dec. 22, 1972 [21] Appl. No.: 317,762

[52] US. Cl. 340/251 [51] Int. Cl. G08b 21/00 [58] Field of Search 340/213.2, 251, 256

[56] References Cited UNITED STATES PATENTS 3,633,196 l/l972 Winkler et al. 340/251 3,686,667 8/1972 Schultz 340/409 3,719,937 3/1973 Doyle 340/251 3,745,547 7/1973 Hadank 340/251 Primary ExaminerDonald J. Yusko Attorney, Agent, or FirmFriedman & Goodman [57] ABSTRACT A lamp failure detector assembly includes a plurality of lamp filament sensors. Each lamp filament sensor includes a switching circuit which is connected to an associated pilot lamp to be monitored and to a transducer which is capable of assuming one of two states. In one state of the transducer, the switching circuit causes a current having one level to flow through the lamp, the level being sufficient to visibly light the lamp. 1n the other state of the transducer, the switching circuit causes a current to flow through the lamp which is insufficient to visibly light the lamp. A control circuit is connected to the pilot lamp to be monitored the control circuit being so arranged so as to cause a monitoring current to flow through the pilot lamp when the filament of the latter is good irrespective of the state of the transducer, the monitoring current which passes through the bulb and through the control circuit having a level sufficient to be detected by the control circuit yet insufficient to visibly light the lamp. Each control circuit of a respective lamp filament sensor is arranged to sense the level of current flow through an associated pilot lamp and for generating a control signal when current flow through the pilot lamp is interrupted. A failure sensing circuit is connected to each of the control circuits for receiving a control signal-when one of the monitored pilot lamps fails and for energizing a failure indicator lamp as well as an audible alarm device. A ring-back circuit connected to the' failure sensing circuit is connectable to the audible alarm device so that when the audible alarm device is connected to the ring-back circuit while one of the monitored pilot lamps is faulty, the audible alarm device is not energized. When the faulty pilot lamp is replaced by a good lamp, the failure sensing circuit and the ring-back circuit change their respective states so that the failure indicator lamp is deenergized and the audible alarm device is energized. The latter energization of the audible alarm device is termed the ring-back and gives an indication that a faulty bulb has been replaced by a good one the ringing back being continued until the audible alarm device is again connected to the failure sensing circuit.

5 Claims, 4 Drawing Figures s.. i SWI CHING CIRCUIT ALARM DEVICE AUDlBLF CIRCUIT PAIENTEIIJIIL23I9I I 3,825,914

SNEUIUF G T U w I 8 I 1 6| I I2 I 66 I io I SWITCHING 26 CO TROLv & I O

I CIRCUIT c c I I l I 68 84 I 1 I9 \AL I 80 L f J I"-----" "-7 I B+ I14 I SWITCHING 46 CONTROL y I CIRCUIT CIRCUIT II I 76 i I l I 59 78 7| 1 1 \N I VI a I L- g 1 fl a 5 n g g SWITCHING I46 CONTROL LP O I I CIRCUIT CIRCUIT 2 I I I76 I78 ITI I I39 I I T Sb 2 FAILURE AUD|BLE SENSING ALARM I04 06 CIRCUIT DEVICE 94 O I08 I 86 I20 I02 L RING-BACK E CIRCUIT Fl G. If

LAMP FAILURE DETECTOR ASSEMBLY BACKGROUND OF THE INVENTION The present invention generally relates to monitoring circuits, and more particularly to a lamp failure detector assembly suitable for monitoring a plurality of lamps simultaneously and for providing both visible as well as audible information when a pilot lamp which is monitored becomes faulty. A ring-back feature is provided which provides audible information when the faulty bulb has been replaced by a good bulb.

Monitoring systems of various types are already known. For example, it is common to monitor the operation of components in a circuit to insure continued proper operation thereof. This is especially true when the appearance of the component does not change in appearance between its normal and its inoperable conditions. However, many of the known monitoring assemblies are complex and costly to manufacture. This is especially true in cases where numerous components must be simultaneously monitored.

For example, indicator lamps are frequently utilized in connection with multi-station intercom systems to provide an indication of which stations are in communication with one another. Also, indicator lights are commonly utilized in conjunction with burglar and fire detection systems, wherein master panels are provided with a plurality of lamps to indicate the numerous normal and alarm conditions. Further, indicator lamps are very frequently utilized in electronic equipment to indicate the on-off conditions of components, assemblies or sub-assemblies.

The present invention for a lamp failure detector assembly is suitable for monitoring the lamps in any of the above-mentioned equipment. The monitoring function which the present invention provides is important because frequently a burned out light appears to give a particular type of condition when, in reality, the other condition exists but cannot be communicated to an observer due to a faulty or burned out lamp or bulb. Failure of an indicator lamp may be critical where the function monitored is an important one. For example, indicator bulbs in automobiles which indicate the oil pressure in the engine must always be operative if engine damage is to be prevented. However, because of the unavailability of suitable monitoring means in the prior art, indicator bulbs in automobiles, as well in other equipment, has hitherto been unmonitored.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a lamp failure detector which does not have the disadvantages possessed by similar prior art detec- It is yet another object of the present invention to provide a lamp failure detector which includes means for testing the operability of the pilot lamps which are monitored.

It is a further object of the present invention to provide a lamp failure detector assembly wherein a plurality of pilot lamps are simultaneously monitored without interference of one filament sensor monitoring one pilot lamp with the other filament sensors monitoring the other lamps.

It is still a further object of the present invention to provide a lamp failure detector for monitoring a pilot lamp while the latter is fully operable to indicate the state of a remote transducer.

It is yet a further object of the present invention to provide a lamp failure detector of the type presently under discussion which includes a ring-back means suitable for sounding an audible alarm once a faulty lamp has been replaced by a good lamp.

Accordingly, in order to achieve the above objects, as well as others which will become apparent hereafter, the lamp failure detector for monitoring at least one pilot lamp arranged to show the state of a transducer comprises at least one lamp filament sensor connected to a lamp. The lamp filament sensor includes input terminal means adapted to be connected to a transducer capable of assuming first and second states. Switching means also forms part of said lamp filament sensor and is connected to said input terminal means and to the lamp for controlling the magnitude of the current flowing through the lamp between two levels as a function of the state of the transducer. One level of the current flowing through the lamp is sufficient to visibly light the lamp while an other level of current is insufficient to visibly light the lamp. Control means, also forming part of said lamp filament sensor, is provided for sensing the level of current flow through the pilot lamp and for generating a control signal when current flow through the pilot lamp is interrupted. Failure sensing means is provided and connected to said control means for receiving said control signal. Indicator means are provided and connected to said failure sensing means for providing an indication when current flow is interrupted in the pilot lamp and a control signal is received by said failure sensing means.

According to a presently preferred embodiment, a plurality of pilot lamps are to be simultaneously monitored and a plurality of lamp filament sensors are provided, each respectively connected to an associated pilot lamp. All said lamp filament sensors are connected to said failure sensing means. Each lamp filament sensor is arranged to generate a control signal receivable by said failure sensing means when the current in a respective pilot lamp is interrupted. In this manner, an indication is provided whenever any lamp filament fails and prevents current flow therethrough.

Said control means is connected to said one pilot lamp and is arranged to cause a monitoring current to flow through said one pilot lamp when the filament of the latter is good. Said monitoring current has a level sufficient to be detected by said control means yet insufficient to visibly light the lamp.

According to another advantageous feature of the present invention, ring-back means are provided, said indicator means comprising an audible alarm device switchably connected to said failure sensing means and to said ring-back means. Said failure sensing means and connected to said ring-back means.

BRIEF DESCRIPTION OF THE DRAWINGS With the above and additional objects and advantages in view, as will hereinafter appear, this invention comprises the devices, combinations and arrangements of parts hereinafter described and illustrated in the accompanying drawings of a preferred embodiment in which:

FIG. 1 is a block diagram of the lamp failure detector assembly in accordance with the present invention, showing three lamp filament sensors associated with three respective pilot lamps to be monitored;

FIG. 2 are schematic diagrams of two of the lamp filament sensors of FIG. 1; I

FIG. 3 is a schematic diagram of the failure sensing circuit and the ring-back circuit of FIG. 1; and

FIG. 4 is a schematic diagram of one lamp filament sensor in accordance with another embodiment thereof.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the FIGURES, wherein similar or identical components have been designed by the same reference numerals, and first referring to FIG. 1, a block diagram of the lamp failure detector assembly is shown and designated by the reference numeral 10. The lamp failure detector assembly is shown to comprise three lamp filament sensors 12, 14 and 130. Although three lamp filament sensors have been shown, it should be pointed out that any number of lamp filament sensors may be provided the number possibly ranging from one to any desired number, as will become apparent hereafter. Each lamp filament sensor is identical in construction to the other lamp filament sensor and therefore it is only necessary to specifically describe the construction of one such sensor.

The lamp filament sensor 12 includes a switching circuit 19 whose specific construction as well as function will be more fully described in connection with FIG. 2. The switching circuit 19 has an input terminal which is connectable in a conventional manner to a transducer (not shown). The specific transducer utilized is not critical for the purpose of the present invention. As suggested in the Background of the Invention, the transducer may originate in an intercom system, in an automobile oil pressure test circuit, and electronic control board, etc. In each case, the transducer connected to the switching circuit can generally assume one of two states. A pilot lamp or bulb 26 is connected to the switching circuit 19 and is so associated with the latter, as to be described hereafter, so that when the transducer changes states, the lamp 26 becomes energized or deenergized, as the case may be.

Connected to the pilot lamp to be monitored is a control circuit 61 whose function is to monitor current flowing through the lamp 26. The switching circuit 19 is so arranged in relation to the lamp 26 so that the current in the lamp 26 may change between two levels as a function of the state of the transducer. One level of the current through the lamp 26 is sufficient to visibly light the lamp while the other level of current is insufficient to visibly light the lamp. Whether one or the other level of current is caused to flow through the lamp 26 is primarily determined by the switching circuit 19.

Independently of the switching circuit 19, the control circuit 61 causes a monitoring current to flow through the pilot lamp 26 so long as the filament of that pilot lamp is good. The monitoring current which passes through the lamp 26 has a level sufficient to be detected by the control circuit 61, yet insufficient to visibly light the lamp 26.

So long as a current is detected in the lamp 26 by the control circuit 61, the output of the control circuit 61 is maintained at a low level, as will be more further described hereafter. When current is interrupted in any pilot lamp, its associated control circuit generates a control signal, to be more specifically described hereafter.

Similarly, the switching circuit 39 and the control circuit 71 are connected to the lamp 46 while the switching circuit 139 and the control circuit 171 are connected to the pilot lamp 146. The outputs of the control circuits 61, 71 and 171 are each connected to a failure sensing circuit 89 through respective isolating diodes 66, 76 and 176. Also connected to the failure sensing circuit 89 via respective isolating diodes 68, 78 and 178 are one terminal of each of the pilot lamps 26, 46, 146 while the other respective terminals of the lamps are connected to the source of potential B+.

When a control signal is generated by any one of the control circuits, the control signal is applied to the failure sensing circuit 89 via an associated isolating diode the failure sensing circuit 89 energizing the failure indicator lamp 94. An audible alarm device 120, being connected to a movable contact 104 of a two-position switching 102, is simultaneously energized when the movable contact 104 is engaged with a fixed contact 106 connected to the failure sensing circuit.

A ring-back circuit 99 is connected to the failure sensing circuit 89 and also connected to a fixed contact 108 of the switch 102. When the movable control 104 is engaged with the fixed contact 108, while a control signal is generated by any of the control circuits, the audible alarm device 119 is deenergized, as to be further described hereafter. However, as soon as a faulty bulb is replaced and none of the control circuits generates a control signal, the ring-back circuit energizes the audible alarm device this being termed ringback until the movable contact 104 is again engaged with the fixed contact 106.

The lamps 26, 46 and 146 are each connected to a source of potential B+ and to a common test buss or line 88 via associated diodes 68, 78 and 178. The line 88 is connected to a normally open momentary contact switch 86 at one terminal thereof while the other terminal of the switch is grounded. By momentarily closing the switch 86, currents are caused to flow in each of the pilot lamps being monitored of sufficient magnitude or level so as to light the same. Simultaneously, the switch 86, also being connected to the failure sensing circuit 89, via line 88' causes the lamp 94 as well as the audible alarm device 120 to be energized to signify that a test is being performed for the purpose of determining which, if any, of the lamps being monitored are faulty.

The circuit associated with the block diagram of FIG. 1 will now be described in more detail by way of specific embodiments which are, however, merely illustrative. It will become apparent from a description of the specific circuitry that numerous variations are possible which function similarly to the circuits to be described. All minor variations which will be evident to one skilled in the art are also contemplated to be included within the scope of the invention.

Referring to FIG. 2, the switching circuit 19 of FIG. 1 is shown to comprise a switching stage including an NPN transistor 20 whose emitter is connected to the circuit ground. The base of the transistor is connected to a center tap 23 of a voltage divider consisting of series connected resistors 22 and 24, the latter two transistors being connected in series between a source of energy in the form of a power supply having a potential 3+ and the circuit ground. Connected between the center tap 23 and a transducer (not shown) which may be remote, is a relay 30 having a coil 32. One terminal 7 of the coil 32 is advantageously connected to the circuit ground while the other terminal of the coil 32 is connectable to the transducer whose state is to be indicated by a bulb or pilot lamp 26. The pilot lamp 26 is connected between the power supply voltage 8+ and the collector of the transistor 20. The coil 32 of the relay 30 cooperates with a movable contact 34 and two fixed contacts 36 and 38.

The switching circuit 19 of the lamp failure sensor 12 described thus far functions to regulate the level of current which may flow through the pilot'lamp 26 as a function of the state of the transducer which is connected to the coil 32. Thus, when the transistor 20 is on or conducting, the collector of the transistor 20 is placed at a relatively low potential level and the substantial part of the power supply potential 8+ is placed across the pilot lamp 26. Thus, a conducting transistor 20 causes a level of current to flow through the pilot lamp 26 which is sufficiently high so as to visibly light the pilot lamp 26. Advantageously, the pilot lamp 26 is so selected so that the level of current which flows therethrough when the transistor 20 is conducting is the rated current for the lamp 26 to thereby provide the maximum brightness when the switching circuit 19 is energized.

When the transistor 20 is off or non-conducting, the current flowing through the pilot lamp 26 is reduced to a level which cannot visibly light the lamp. As should be clear, if only the pilot lamp 26 were connected to the collector of thetransistor 20, the turning off or making the transistor 20 non-conductive would fully interrupt the current flow in the pilot lamp 26. However, the current through the pilot lamp does not drop to zero as a result of the control circuit stage 61 of FIG. 1, as to be described hereafter. I

The conductive and non-conductive stages of the transistor 20 are controlled or regulated by a usually remote transducer connected to an actuatable means which, in FIG. 1, is in the form of the relay 30. The relay 30 is so selected so that a movable contact 34 is normally, i.e. when the coil 32 is not energized, connected to a contact 38 which is connected to the center tap 23. When the coil 32 is energized, the movable contact 34 is moved into engagement with a fixed contact 36 which is left-floating.

In the normal states of the transducers, accordingly, the bases of the switching stage transistors 20, 40, etc. are placed at ground potential or the same potential as the emitters of said transistors. The switching stage transistors are thereby non-conductive and the pilot lamp 26, 46, etc., are not visibly lit. Should the coil 32 be energized by the application of a potential thereto in a conventional manner by a remote transducen'the 5 relay 30 is energized and the movable contact 34 disengages from the fixed contact 38 to thereby remove the ground potential from the base of the transistor 20. Once the ground potential is removed from the base of the transistor 20, the voltage divider, consisting of resistors 22 and 24, determines the potential applied to the base of the transistor 20 relative to its emitter. The values of the resistors 22, 24 are so selected so as to supply a sufficiently positive biassing voltage to the base of the transistor 20 so as to make the transistor 20 fully conductive. Simultaneously, the pilot lamp 26 becomes visibly lit as described above. As soon as the transducer reverts to its original or normal state, the coil 32 is again deenergized and the base of the transistor 20 is again grounded. In this manner, the pilot lamps 26, 46, etc., indicate the states of their associated transducers.

Although only two of the lamp filament sensors 12, 14 of FIG. 1 are shown, it should be clear that any number of lamp filament sensors may be provided to correspond with as many pilot lamps 26, 46, etc. as are to be monitored. In each case, the construction of the switching circuits 19, 39 and 139 described above may be identical.

As described above, the switching circuit transistors regulate the level of the current flowing through the pilot lamps being monitored. The current flowing through the lamps may be switched from an approximately rated current to approximately a zero current depending on the conductive or non-conductive state of the associated switching stage transistor. An important feature of the present invention is the maintenance of a slight monitoring current through the pilot lamps to be monitored irrespective of the states of the switching stage transistors and always monitoring the current flowing through the pilot lamps as an indication of their respective operabilities or filament conditions. Thus, so long as a current can be made to flow through a pilot lamp, this is an indication that the pilot lamp is in good operating order. However, as soon as a current, however slight, cannot be passed through a pilot lamp, this is an indication that the pilot lamp is faulty and must be replaced.

In FIG. 1, control circuits 61, 71, 171 are each shown connected to an associated pilot lamp for monitoring current flow therethrough. In FIG. 2, the control circuit 61 is shown to comprise a control stage NPN transistor 62 whose collector is connected to the energy supply having a potential of B-lthrough a load resistor 64. The emitter of the transistor 62 is grounded while the base of the transistor is connected to the collector of the transistor 20 by means of a current limiting resistor 60. Each of the control circuits associated with a different pilot lamp is similarly constructed. The value of the resistor 60 is so selected so as to prevent excessive current flow through the base-emitter junction of the transistor 62 which may damage said transistor. However, the resistor 60 is selected to have a value sufficiently low so as to permit a monitoring current to flow through the pilot lamp 26, the resistor 60, and the baseemitter junction of the transistor 62. The monitoring current must be one which is sufficiently small so as not to visibly light the lamp 26 while being sufficiently large so as to be capable of detection by the control stage transistor 62. Otherwise stated, the monitoring current which flows through the lamp 26 and the transistor 62 must be sufficiently large so as to provide base current to the transistor which will maintain the transistor 62 in a conductive state so long as the monitoring current is permitted to flow. Thus, the potential at the control stage transistor 62 base must be maintained at a sufficiently positive voltage and a sufficiently large base current must be available in order to maintain the transistor on or conductive whenever the pilot lamp 26 conducts a current. When the transistor is not con ductive, the potential at the collector of the transistor 20 becomes highly positive and sufficient base current is provided to maintain the control stage transistor 62 conductive. However, when the transistor 20 becomes conductive, the collector-emitter saturation voltage is approximately one volt the value of resistance of the resistor being selected to provide sufficient base current for the transistor 62 when the collector voltage of the transistor 20 is at its lowest contemplated positive level. Thus, the lower limit for the resistor 60 value is determined by the maximum transistor 20 collector potential andthe maximum base current which can be safely supplied to the transistor 62 while the upper limit of the resistor 60 resistance value is determined by the minimum anticipated transistor 20 collector voltage as well as the minimum transistor 62 base current which is sufficient to maintain the latter transistor in a conductive state.

From the above, it should be clear that so long as the filament of the pilot lamp 26 is not burned out or as long as the lamp is operable, sufficient positive potential and base current will be provided at the base of the transistor 62 to maintain the same conductive. Accordingly, the potential at the collector of the transistor 62 will be maintained at a low level. However, as soon as a filament, e.g. the filament of the lamp 26, burns out or the pilot lamp becomes faulty and no further current can flow therethrough, the conductive connection between the positive supply voltage B+ and the collector of the transistor 20 as well as the base of the transistor 62 is interrupted and no positive potential can be applied thereto. As soon as positive potential is removed from the base of the control stage transistor 62, the latter transistor becomes non-conductive and the collector thereof rises substantially towards the power supply potential B+. It should be clear that as soon as any one of the pilot lamps being monitored becomes faulty, its associated control stage transistor collector rises in potential. The normally low collector potentials of the control stage transistors are termed no control signal conditions while the rise in collector potential in the manner described in connection with a faulty bulb is termed generation of a control signal by the associated control circuit. As described in connection with FIG. 1, all the control circuits are connected by respective lines, e.g. line of the lamp filament sensor 12, to a lamp failure signal'buss 82. Referring to FIGS. 2 and 3, the lamp failure signal buss is connected to the base of a failure sensing stage transistor 90. The collectors of the respective control stage transistors 62, 72, etc. are connected to the base of the transistor via respective isolating diodes 66, 76, etc. The isolating diodes are so arranged so that the generation of a positive control signal at the collectors of the control stage tansistors are transmitted to the base of an NPN transistor 90. However, when the control stage transistors 62, 72, etc. are normally conductive, when their associated bulbs are operable, the collector voltages of the respective control stage transistors are sufficiently low so that 5 the potentials applied to the lamp failure signal buss 82,

in view of the additional voltage drop across the isolating diodes, are insufficient to cause the transistor 90 to become conductive when its emitter is grounded. However, when a control signal is generated, i.e. the base of a control stage transistor rises in response to failure of an associated pilot lamp, the control signal becomes sufficient, even with the isolating diode voltage drop, for making the transistor 90 conductive.

The transistor 90 forms part of the failure sensing circuit 89 as shown in FIG. 1. The failure indicator lamp 94 is connected between the collector of the sensing stage transistor 90 and the power supply potential B+. As similarly described in connection with the switching stage transistors, when the sensing stage transistor 90 is conductive, sufficient current is permitted to flow through the failure indicator lamp 94 so as to make the same visibly lit. However, when the failure sensing stage transistor 90 is non-conductive, insufficient current flows through the lamp 94 and the latter is not visibly lit.

The ring-back circuit 99 as shown in FIG. 1 comprises a ring-back stage NPN transistor 100 whose emitter is grounded. Series connected resistors 96, 98 form a voltage devider having a center tap 97. The series connected resistors are connected between the collector and emitter of the transistor 90. The base of the ring-back stage transistor 100 is connected to the center tap 97 Thus, when the transistor 90 is nonconductive, the collector-emitter voltage of the transistor 90 is sufficiently large so as to provide a potential at the center tap 97 which tends to make the ring-back stage transistor 100 conductive. On the other hand, when the transistor 90 is conductive, the collectoremitter voltage thereof is very low and the potential at the center-tap 97 is insufficient to tend to cause the transistor 100 to be conductive. Thus, it should be clear that the transistors 90 and 100 are so arranged so as to operate complementarily to one another so that when one transistor is conducting the other is not and vise versa. A two position switch 102 is provided having a movable contact 104, a fixed contact 106 connected to the collector of the transistor 90 and a fixed contact 108 connected to the collector of the transistor 100. The fixed contact 106 will be termed the normal position of the switch while the contact 108 will be termed the ring-back or the silent position.

Connected to the movable contact 104 is a coil 109 of a relay 110. The coil 109 represents a load which is switchable between the contacts 106 and 108. When the movable contact engages the contact 106, the coil 109 becomes a load of the transistor 90 parallel with the failure indicator lamp 94. When the movable contact 104 is engaged with the fixed contact 108, the coil 109 becomes a load of the transistor 100.

r The coil 109 cooperates with the contacts 112, 114 and 116 of the relay to control the operation of the audible alarm device 120.

The movable contact 104 is normally in contact with the fixed contact 106 in the so-called normal position. In the normal position of the switch 102, the operation of the relay 110 is controlled by the failure sensing transistor 90. Accordingly, when the failure sensing transistor 90 is non-conducting, the coil 109, similarly to the failure indicator lamp 94, is not energized and the relay contacts are so arranged so that the movable contact 112 is engaged with the floating fixed contact 114. Accordingly, the audible alarm device 120 will similarly be deenergized.

With the switch 102 still in its normal position, when the failure sensing stage transistor 90 becomes energized, its collector potential drops to substantially the saturation voltage of the transistor and the failure indicator lamp 94 as well as the coils 109 become energized. Accordingly, the lamp becomes visibly lit and the movable contact 112 engages the grounded fixed contact 116 to thereby energize the audible alarm device 120.

When the switch 102 is movedto its ring-back or silent position, wherein the movable contact 104 engages the fixed contact 108, the failure indicator lamp 94 and the audible alarm device 120 operate out of phase. Thus, with the switch 102 in the ring-back position,

when the transistor 90 is non-conductive the indicator 1 lamp 94 is not visibly lit while the coil 109 is energized due to the conductive state of the ring-back transistor 100. Thus, while the failure indicator lamp is deenergized the audible alarm device 120 is energized. On the other hand, when the failure sensing stage transistor becomes energized, the failure indicator lamp 94 becomes visibly lit while the coil 109 becomes deenergized due to the now non-conductive ring-back transistor 100. Now, while the failure indicator lamp 94 is visibly lit, the audible alarm device 120 is deenergized.

The isolating diodes 66, 76, etc., respectively connected to the control circuit transistors 62, 72, etc., are advantageously provided as shown in FIGS. 1 and 2 for the purpose of isolating the collectors of the respective control stage transistors. In the absence of the control isolating diodes 66, 76, etc., the generation of a control signal in the form of a rising potential at one of the control stage transistor collectors, may be loaded by the other still heavily conducting control stage transistors. Such interference may prevent the rise of voltage at the base of the transistor 90 sufficiently'to make the latter conductive.

In accordance with another feature of the present invention, means are provided for simultaneously testing all the pilot lamps being monitored to determine which, if any, of the lamps is faulty. Referring to FIGS. 1 and 2, each switching circuit has associated therewith, a switching isolating diode 68, 78, 178, etc., are all connected to a common lamp test buss 88 via individual lines, e.g. line 84 associated with the isolating diode.68. The common lamp test buss 88 is connected to the circuit ground by way of a normally open momentary contact switch 86. The common lamp test buss 88 is also connected, via line 88 and an isolating diode 92, to the collector of the failure sensing stage transistor 90. Closing of the momentary contact switch 86 grounds the collectors of all of the switching transistors 20, 40, etc., this simulating the conductive states of said transistors. Thus, so long as the momentary contact switch 86 is maintained in a closed position, all of the pilot lamps being monitored are simultaneously energized and made visibly lit. It is now possible by an observer to determine which, if any, of the pilot lamps are faulty. It is clear that all but the faulty pilot lamps will become visibly lit when the momentary contact switch is closed.

The switch and isolating diodes 68, 78, etc., serve two functions. Firstly, the switching isolating diodes isolate the respective collectors of the various switching stage transistors 20, 40, etc., from each other. Such isolation is necessary if the bases of the control stage transistors 62, 72 etc., are to be deprived of potential and base current upon failure of an associated pilot lamp. Deletion of the switching isolating diodes would result in application of potential as well as the provision of current from one lamp failure sensor to another lamp failure sensor via the common lamp test buss despite the failure of a pilot lamp. Thus, the switching isolating diodes 68, 78, etc., assure that the control stage transistors become non-conductive when their associated pilot lamps become faulty.

Secondly, switching isolating diodes 68, 78 serve the further function of maintaining somewhat positive voltages at the collectors of the switching stage transistors 20, 40, etc., equal to the voltage drop across said switching isolating diodes. These somewhat positive voltages at the collectors of the switching stage transistors may be sufficient to maintain the control stage transistors 62, 72, etc., conductive despite the grounding of the common lamp test buss 88.

The common lamp test buss 88 is also connected to the collector of the failure sensing stage transistor 90 via the isolating diode 92 as described above. The effect of closing the momentary contact switch 86 grounds the collector of the transistor 90 this simulating theconductive state of the transistor. Accordingly, the failure indicator lamp 94 will become energized independently of the conductive states of the control stage transistors or the state of the failure sensing stage transistor 90. Similarly, if the switch 102 is in its normal position, the audible alarm device will become energizedlf the switch 102 is in the ring-back position or silent position, closing of the momentary contact switch 86 will cause the audible alarm device to become deenergized so long as the momentary contact switch is maintained in a closed state.

In FIG. 4, a lamp filament sensor 12' is shown which is another embodiment of the lamp failure sensor 12 of FIG. 2. In FIG. 4, the relay 30 of FIG. 2 has been replaced by a transistor'circuit generally designated by the reference numeral 200. The transistor circuit 200, similarly to the relay 30, constitutes actuatable means which are connectable to a remote transducer. The transistor circuit 200 comprises a transistor 202 whose collector is connected to the center tap 23 and whose emitter is connected to the circuit ground. The base of the transistor 202 is connected to a center tap 203 of a voltage divider comprising resistors 204, 206 which are series connected with each other and connected between the positive supply potential B+ and the circuit ground. The base of the transistor 202 is connectable to a remote transducer as was the one terminals of the coil 32. In connection with this actuating means 200, the remote transducer advantageously grounds the base of the transistor 202 when it changes from one state to another. Accordingly, when the base of the transistor 202 is grounded, the transistor 202 is nonconductive and the potential of the center tap 23 is determined by the voltage divider resistor 22, 24 the potential formed at the center tap being sufficient to make the transistor 20 conductive. When the transducer changes states and ungrounds the base of the transistor 202, a potential is applied to the base of the transistor as determined by the values of the resistors 204, 206. The potential at the center tap 203 is advantageously selected so that when the base of the transistor 202 is not grounded, the transistor becomes conductive to thereby ground the base of the transistor 20 and causing the latter to become non-conductive. In all other respects, the lamp failure sensor 12' is similar and functions similarly to the lamp failure sensor 12. As will be evident to those skilled in the art, numerous other forms of actuatable means can be substituted for the relay 30, or the transistor circuit 200.

The operation of the lamp failure detector assembly, to the extent to which it has not been set forth above, will now be described. In describing the operation, it will be assumed that the lamp failure detector assembly merely comprises two lamp filament sensors 12 and 14. However, as has already been made clear above, any number of lamp filament sensors may be provided each respectively connected to the lamp failure signal buss 82 and the common lamp test buss 88 as described above. First it will be assumed that the pilot lamps 26, 46 are both operative. When neither of the coils 32, 52 are energized, the transistors 20, 40 are nonconductive. Accordingly, the monitoring currents which flow through the lamps 26, 46 are insufficient to visibly light the lamps. However, the monitoring currents passing through the pilot lamps are sufficient to maintain the control stage transistors 62, 72 respectively in a conductive state. As described above, this represents a no signal condition on the lamp failure signal buss 82 and the failure sensing stage transistor 90 is non-conductive, with the attendant non-energized states of the failure indicator lamp 94 and audible alarm device 120 (when the switch 102 is in its normal position in engagement with the fixed contact 106).

When a remote transducer energizes a coil, e.g. coil 32, the transistor 20 is made conductive and a current is permitted to flow to the pilot lamp 26 of sufficient level to make the pilot lamp visibly lit. However, as described above, the potential at the collector of the transistor 20 is sufficiently positive so that the conditions at the base of the control stage transistor 62 are still such as to make the latter transistor conductive as before change of states of the transducer. Accordingly, the change of states of the transducer merely effects the conductive states of the switching stage transistor 20 and does not regulate the control circuit 61 and the circuitry beyond.

It is noted that while all the control stage transistors are conductive, the failure sensing stage transistor 90 is non-conductive and the ring-back stage transistor 100 is conductive. Thus, while the failure indicator lamp 94 is deenergized, the audible alarm device 120 may be energized if the movable contact 104 is moved from its normal position into engagement with the fixed contact 108.

Similarly, if the coil 52 is energized instead of the coil 32, the switching stage transistor 40 becomes conductive and the pilot lamp 46 becomes visibly lit. As before, the control stage transistor 72 remains energized and fails to generate a control signal which can energize the transistor 90. If both coils 32 and 52 are simultaneously energized, in any conventional manner, then both transistors 20 and 40 become energized and pilot lamps 26 and 46 become visibly lit. Again, the control stage transistor 62, 72 remain conductive and no control signals are generated.

hold true with respect to any other pilot lamp so being monitored. As soon as the pilot lamp 26 becomes faulty, the source of positive potential at the collector of the transistor and the base of the transistor 62 is removed. This results from the open circuit now existing between the source of positive potential B+ and the collector of the transistor 20. With no voltage and current applied to the base of the transistor 62, the control stage transistor 62 becomes non-conductive and its collector rises towards the B+ potential. This constitutes, as described above, a control signal which is transmitted through the control isolating diode 66 via the lamp failure signal buss 82 to the base of the transistor 90.

. The application of a positive control signal to the base of the failure sensing stage transistor makes the latter transistor conductive with atendant energization of the failure indicator lamp 94. Since the switch 102 is normally set so that the movable contact 104 is engaged with the fixed contact 106, the generation of a control signal simultaneously energizes the coil 109 and the audible alarm device 120.

Although the function of monitoring pilot lamps and providing indicator means for indicating a faulty condi tion of a monitored pilot lamp has thus been accomplished, another feature of the present invention consists in providing a ring-back or other suitable indication when a faulty bulb has been replaced by a good or operable bulb. In accordance with this feature, as soon i as the failure indicator lamp 94 becomes visibly lit and the audible alarm device 120 becomes audible, the switch 102 is changed in state so that the movable contact 104 engages the fixed contact 108. As described above, so long as a faulty pilot lamp is monitored, the failure sensing transistor stage 90 is conductive. Accordingly, during this time, the ring-back stage transistor is non-conductive as described above. Consequently, moving the switch 102 while the audible alarm device is energized to the ring-back or silent position deenergizes the audible alarmdevice. At this time, while a faulty bulb is being detected, the failure indicator lamp 94 is energized while the audible alarm device is deenergized.

When the faulty pilot lamp 26 is replaced by a good pilot lamp which can conduct the requisite monitoring current to the base of the transistor 62, the control signal on the lamp failure signal buss 82 is removed and the transistor 90 becomes non-conductive while the ring-back transistor 100 becomes conductive. Accordingly, when a faulty lamp is replaced by a good one, the failure indicator lamp 94 becomes deenergized while the audible alarm device 120 becomes energized to provide a ring-back audible signal denoting that such lamp replacement has taken place. At this time, the switch 102 is again moved to its normal position to deenergize the audible alarm device 120. The lamp failure detector assembly is now reset to its original standby position for monitoring a further possible failure of a pilot lamp being monitored.

As described above, once failure of a lamp is indicated, the momentary contact switch 86 can be momentarily closed to determine which pilot lamp is faulty since all the lamps except the faulty ones will become visibly lit on the closing of the switch.-

Numerous alterations of the structure herein disclosed will suggest themselves to those skilled in the art. However, it is to be understood that the present disclosure relates to a preferred embodiment of the invention which is for purposes of illustration only and is not to be construed as a limitation of the invention.

What is claimed is:

1. Lamp failure detector for monitoring at least one pilot lamp arranged to show the state of a transducer, said detector comprising at least one lamp to be monitored; switching means connected to said lamp for controlling the magnitude of a signal current flowing through said lamp between two levels, one level being sufficient to visibly light the lamp and another level insufficient to visibly light the lamp; control means for sensing the level of current flow through said lamp and for generating a control signal when current flow through said lamp is interrupted; failure sensing means comprising a transistor having a base connected to said control means for receiving said control signal; indicator means comprising an audible alarm device connected to the collector of said transistor for providing an indication when current flow is interrupted in said lamp and a signal is received at said base of said transistor; ring-back means connected to said collector of said transistor; and movable contact means for switching said audible alarm device to said collector of said transistor and to ring-back means, said failure sensing means and said ring-back means being arranged in cooperative relation with one another to energize said audible alarm device when connected to said collector only when a control signal is generated while only being between said collector of said failure sensing means transistor and the emitter of the latter, said ring-back transistor having a base connected to said center tap and a collector to which said audible alarm device can be switched.

4. Lamp failure detector as defined in claim 3, further comprising a two-position switch having a movable contact connected to said audible alarm device, a first fixed contact connected to said collector of said failure sensing transistor means, and a second fixed contact connected to said collector of said ring-back means, said audible alarm device being arranged to be energized only when connected to said first contact in the presence of a control signal while being arranged to be energized only when connected to said second contact in the absence of a control signal.

5. Lamp failure detector for monitoring at least one pilot lamp arranged to show the state of a transducer, said detector comprising at least one lamp to be monitored; switching means connected to said lamp for controlling the magnitude of a signal current flowing through said lamp between two levels, one level being sufficient to visibly light the lamp and another level insufficient to visibly light the lamp; control means for sensing the level of current flow through said lamp and for generating a control signal when current flow through said lamp is interrupted; failure sensing means connected to said control means for receiving said control signal; indicator means connected to said failure sensing means for providing an indication when current flow is interrupted in said lamp; ring-back means connected to said failure sensing means; and movable contact means for switching said indicator means to said failure sensing means and to said ring-back means, said failure sensing means and said ring-back means being arranged to energize said indicator means when connected to said failure sensing means only when a control signal is generated while only being energized in the absence of a control signal when connected to said ring-back means. 

1. Lamp failure detector for monitoring at least one pilot lamp arranged to show the state of a transducer, said detector comprising at least one lamp to be monitored; switching means connected to said lamp for controlling the magnitude of a signal current flowing through said lamp between two levels, one level being sufficient to visibly light the lamp and another level insufficient to visibly light the lamp; control means for sensing the level of current flow through said lamp and for generating a control signal when current flow through said lamp is interrupted; failure sensing means comprising a transistor having a base connected to said control means for receiving said control signal; indicator means comprising an audible alarm device connected to the collector of said transistor for providing an indication when current flow is interrupted in said lamp and a signal is received at said base of said transistor; ring-back means connected to said collector of said transistor; and movable contact means for switching said audible alarm device to said collector of said transistor and to ring-back means, said failure sensing means and said ring-back means being arranged in cooperative relation with one another to energize said audible alarm device when connected to said collector only when a control signal is generated while only being energized in the absence of a control signal when connected to said ring-back circuit.
 2. Lamp failure detector as defined in claim 1, wherein said indicator means further comprises a failure indicator lamp.
 3. Lamp failure detector as defined in claim 1, wherein said ring-back means comprises a transistor, first and second series-connected voltage divider resistors having a center tap, said resistors being connected between said collector of said failure sensing means transistor and the emitter of the latter, said ring-back transistor having a base connected to said center tap and a collector to which said audible alarm device can be switched.
 4. Lamp failure detector as defined in claim 3, further comprising a two-position switch having a movable contact connected to said audible alarm device, a first fixed contact connected to said collector of said failure sensing transistor means, and a second fixed contact connected to said collector of said ring-back means, said audible alarm device being arranged to be energized only when connected to said first contact in the presence of a control signal while being arranged to be energized only when connected to said second contact in the absence of a control signal.
 5. Lamp failure detector for monitoring at least one pilot lamp arranged to show the state of a transducer, said detector comprising at least one lamp to be monitored; switching means connected to said lamp for Controlling the magnitude of a signal current flowing through said lamp between two levels, one level being sufficient to visibly light the lamp and another level insufficient to visibly light the lamp; control means for sensing the level of current flow through said lamp and for generating a control signal when current flow through said lamp is interrupted; failure sensing means connected to said control means for receiving said control signal; indicator means connected to said failure sensing means for providing an indication when current flow is interrupted in said lamp; ring-back means connected to said failure sensing means; and movable contact means for switching said indicator means to said failure sensing means and to said ring-back means, said failure sensing means and said ring-back means being arranged to energize said indicator means when connected to said failure sensing means only when a control signal is generated while only being energized in the absence of a control signal when connected to said ring-back means. 